Study On Single-stage Power Factor Correction Techniques

In modern power electronics technology, the bridge rectifier and capacitor filter,characteristics of a mature circuit topology, is widely used in the front of switchingpower supply. It makes the input current distortioned significantly and introducedlarge number of harmonics to the grid, which not only cause a waste of energy, butalso affect the reliable operation of other equipments. So it is needed to calibratepower factors, and reduce the harmonic pollution. With the characteristics of simplestructure, low cost, and easy achievable without adding much devices in manyswitching power supply, the single-stage PFC technology have got a great attention,and become the research focus of PFC technology. For these considerations, thisthesis includes following works:First, the working principles of normal used single stage PFC converters areintroduced and general models are summarized. There exisits three main problem:1) Voltage drop at energy storage capacitor is uncontrollable;2) Voltage stress onswitch is too high;3) The conversion efficiency is much low. Based on analysis of theexiting circuit topology, typical solutions are summed up. Among various solutions,the LCD clamping circuit and the flyboost unit, which exhibit superiority inovercoming all three drawbacks, are highlighted. And working processes are carriedout by analyzing flyback converter.With thus understanding, a new type of single-stage PFC converter is proposed.The new topology combines the LCD circuit and flyboost unit in one flybackconverter. Not only the voltage drops on capacitance and switching can be inhibited,but also the conversion efficiency can be improved. The working principle and controlprocesses are analyzed, and the performances are predicted in this thesis.Based on the previous theoretical analysis, four prototypes are experimentallyconstructed. Flyback, boost, flyboost and new type topology, which have same inputand output characteristics, are used. The main circuit parameters and control circuitstructure are designed in detail, and the magnetic components are properly design andordered lately. Finally, the performances of the four converters are compared bysimulation and experiment measurement. Not only simulation and experimentalwaveforms are presented, but also the typical solution methods which summaried inchapter two are vetified by using the boost converter.From the simulation and experiment results, it can be concluded:1) Flybackconverter has highest power factor, and the voltage drop on energy-storage capacitoris relatively low. But voltage on switch is very high, and efficiency is not as high asexpect, also the stability is much low.2) The power factor and efficiency of boostconverter are relatively low, and have high voltage drop on both the capacitance andswitch.3) The power factor and efficiency of flyboost converter are improved lightly, and its capacitance voltage is inhibited batter, but the voltage on switch is still muchhigh.4) Although the power factor of the new converter is lower than the flyback one,its power factor and efficiency are impored significantly, and the voltage drop onstorage capacitor and switch are kept at a lower value. So it can solve the three majorproblems exited in the other single-stage PFC converters.Finally, the entire research work is summarized and the late research content andmethods are pointed out.